There are two primary reasons for the intentional misspellings. One would be mixing words..."beatles" = "beat" + "beetles". This can be clever, and is not often horrible. Unless it seems forced, like mixing "ska" with other words for ska bands often does. That got real old and real dumb, real fast.

The more common theme now days though is misspelling to be "original". Which isn't very original, considering it's popular. This doesn't just exist in band names -- people who think they're being cool intentionally misspell all sorts of words. "kool" and "kewl" are a couple such misspellings.
There is nothing "kewl" about being illiterate.